1. Field of the Invention
The present invention relates to a webbing take-up device that takes up and accommodates a long band-like webbing belt that restrains the body of a vehicular passenger.
2. Description of the Related Art
Seat belt apparatuses that restrain the body of a passenger with a long band-like webbing belt include a webbing take-up device. The webbing take-up device includes a spool. The longitudinal-direction base end of the webbing belt is attached to the spool. When the spool is rotated in a take-up direction, which is one direction around its axis, the webbing belt is taken up from its base end and accommodated onto the spool.
The webbing take-up device also includes a lock mechanism for locking the spool when a vehicle disposed with the webbing take-up device abruptly decelerates, regulating the pullout of the webbing belt, and restraining the body of the passenger, which tries to move in the substantially forward direction of the vehicle. An example of a webbing take-up device including such a lock mechanism is disclosed in Japanese Utility Model Application Publication No. 62-95058.
In the webbing take-up device disclosed in Japanese Utility Model Application Publication No. 62-95058, a lock ring is disposed coaxially and relatively rotatable with respect to the spool. A lock plate is coupled to the spool between the lock ring and the spool. When the spool relatively rotates in the pullout direction of the webbing belt with respect to the lock ring, the lock plate is displaced outward in the radial direction of turning of the spool and meshes with an inner ratchet formed on a leg plate of a frame. Thus, the spool becomes locked, and the rotation of the spool when the webbing belt is pulled out is regulated.
The lock ring and the spool are coupled together with a torsion coil spring and configured such that the lock ring can rotate following the rotation of the spool due to the biasing force of the torsion coil spring.
That is, the lock ring rotates following the rotating spool when the webbing belt is ordinarily pulled out and taken up. However, when the vehicle abruptly decelerates, the body of the passenger moves in the substantially forward direction of the vehicle. Thus, when the webbing belt is abruptly pulled out and the spool abruptly rotates in the pullout direction, the lock ring cannot follow the spool and the spool relatively rotates in the pullout direction with respect to the lock ring. Thus, as described above, the lock plate meshes with the ratchet of the leg plate, the spool becomes locked, and the pullout of the webbing belt is regulated.
The webbing take-up device also includes a coil spring whose biasing force, which biases the spool in the take-up direction, increases in accompaniment with the rotation of the spool in the pullout direction. The biasing force of the coil spring causes the spool to rotate in the take-up direction when the pulled-out webbing belt is to be taken up.
The lock ring also rotates following the spool when the spool is rotating in the take-up direction in this manner. When the taking-up of the webbing belt onto the spool by the biasing force of the coil spring ends and the spool stops, there is the potential for the lock ring to end up rotating in the take-up direction due to inertia.
In this manner, the situation where the lock ring has rotated in the take-up direction with respect to the spool is the same as the situation where the spool has rotated in the pullout direction with respect to the lock ring. For this reason, even in this state, the lock plate ends up being displaced and meshing with the ratchet of the leg plate.
Because the rotation of the spool in the pullout direction ends up being regulated in this state (so-called “end lock”), the webbing belt that has been taken up and accommodated onto the spool cannot be pulled out.
In the webbing take-up device disclosed in Japanese Utility Model Application Publication No. 62-95058, an end lock preventing mechanism is disposed in order to prevent this drawback.
The end lock preventing mechanism in Japanese Utility Model Application Publication No. 62-95058 includes a cam plate and a function spring that prevent end lock by deterring the relative rotation of the lock ring and the take-up shaft at a predetermined time.
However, the webbing take-up device including this conventional end lock preventing mechanism has a configuration that simply nips a cam plate with a friction spring. For this reason, when the spool abruptly rotates in the take-up direction and takes up the webbing belt, the cam plate pivots due to frictional force that is larger than the frictional force between the friction spring and the cam plate in the state where the friction spring is nipping the cam plate. Thus, there is the potential for end lock to arise.